MrBayes is a program used for bayesian inference of phylogeny. MrBayes is cowritten by John Huelsenbeck and Fredrik Ronquist.
MrBayes uses the NEXUS file format for input. To use MrBayes, just type mb at the command line
[nostromo@rocks-168 mrbayes]$ mb
                               MrBayes v3.1.2
                      (Bayesian Analysis of Phylogeny)
                                     by
                  John P. Huelsenbeck and Fredrik Ronquist
                 Section of Ecology, Behavior and Evolution
                       Division of Biological Sciences
                     University of California, San Diego
                           johnh@biomail.ucsd.edu
                       School of Computational Science
                           Florida State University
                            ronquist@csit.fsu.edu 
              Distributed under the GNU General Public License
               Type "help" or "help <command>" for information
                     on the commands that are available.
MrBayes > | 
A wealth of information about MrBayes is available at the following source - MrBayes Home Page